I. Technical Field
The present invention relates to a hydrodynamic bearing rotary device employing a hydrodynamic bearing, and an information apparatus including the same.
II. Description of Related Art
In recent years, recording apparatuses and the like using discs to be rotated have experienced an increase in memory capacity and an increase in the transfer rate for data. Thus, bearings used for such recording apparatuses are required to have high performance and high reliability to receive a disc and rotate a load constantly with high accuracy. Accordingly, hydrodynamic bearing devices suitable for high-speed rotation are used for such rotary devices.
The hydrodynamic bearing rotary device has a lubricant such as oil between a rotary shaft and a sleeve, and generates a pumping pressure (hydrodynamic pressure) by hydrodynamic grooves during rotation. Thus, the shaft rotates in a non-contact state with respect to the sleeve. Since no mechanical friction is generated, the hydrodynamic bearing rotary device is suitable for high-speed rotation.
Hereinafter, an example of a conventional hydrodynamic bearing rotary device will be described with reference to FIGS. 8 through 10 (see, for example, Japanese Laid-Open Publication No. 2003-88033). As shown in FIG. 8, a conventional hydrodynamic bearing rotary device includes a sleeve 21, a rotary shaft 22, a stopper 23, a bottom plate 24, a lubricant 25, a hub 27, a base plate 28, a rotor magnet 29, a stator 30, and a disc 11.
The rotary shaft 22 is press-fitted to the hub 27. The rotary shaft 22 is inserted into a bearing hole 21A of the sleeve 21 so as to be rotatable. On at least one of an outer peripheral surface of the rotary shaft 22 and an inner peripheral surface of the sleeve 21, radial hydrodynamic grooves 21B are formed to form a radial bearing portion. On a surface of the sleeve 21 opposing the hub 27, thrust hydrodynamic grooves 21D having a spiral pattern as shown in FIG. 9 are formed to form a thrust bearing portion. The bottom plate 24 shown in FIG. 8 is adhered to the sleeve 21. The sleeve 21 has a flange portion 21C on an outer peripheral surface on the side facing the hub. The flange portion 21C has a larger diameter and an outer peripheral surface thereof includes a tapered surface 21E. A seal portion 26 is provided between the tapered surface 21E and a circular protrusion 27A of the hub 27. The stopper 23 having a ring shape is fixed to the hub 27, and is placed so as to oppose the flange portion 21C of the sleeve 21. The lubricant 25 is sealed in the bearing cavity, and a gas-liquid interface is formed near the seal portion 26.
To the base plate 28, the sleeve 21 is fixed. The stator 30 is also fixed to the base plate 28 so as to oppose the rotor magnet 29. To the hub 27, the rotor magnet 29 is fixed, and the disc 11 is fixed by a clamper (not shown). Magnetic centers of the rotor magnet 29 and the stator 30 in an axial direction are largely shifted, and thus, the rotor magnet 29 can generate an attraction force in a direction indicated by arrow A in the figure.
Operations of the conventional hydrodynamic bearing rotary device described above are as follow.
In the conventional hydrodynamic bearing rotary device shown in FIG. 8, when an electric current is supplied to the stator 30, a rotary magnetic field is generated, and a rotary force is applied to the rotor magnet 29. Thus, the rotor magnet 29 starts to rotate with the hub 27, the rotary shaft 22, the stopper 23, and the disc 11. As these members rotate, the radial hydrodynamic grooves 21B gather the lubricant 25 filled in the bearing gap, and a pumping pressure is generated between the rotary shaft 22 and the sleeve 21. In this way, the radial bearing portion functions. The thrust hydrodynamic grooves 21D gather the lubricant 25, and a pumping pressure (a pressure indicated by arrow P in FIG. 8) is generated between the hub 27 and the sleeve 21 in a thrust direction. The rotary part floats in a direction opposite to the attraction force of the rotor magnet 29 which is indicated by arrow A in the figure, and starts to rotate in a non-contact state.
As described above, the rotary shaft 22 can be rotated in a non-contact state with respect to the sleeve 21. With a magnetic head 42 as shown in FIG. 11, data can be recorded/reproduced to/from a rotating disc 11.